1. Field of the Invention
The present invention relates to a range finder mounted on an automatic focusing camera. Specifically, the present invention relates to a module structure of the range finder.
2. Description of Related Art
First, a conventional range finder based on the principle of triangulation using the external light mounted on an auto-focusing camera is explained. FIG. 5 is a block diagram of a conventional range finder based on the principle of triangulation using the external light. Referring now to FIG. 5, the conventional range finder includes an image forming optical system including a pair of range finding lenses 1L, 1R and a semiconductor optical sensor chip 5 including photo-sensor arrays 5L, 5R, quantizer circuits 51L, 51R and a logic circuit 52 integrated into the semiconductor optical sensor chip 5. The photo-sensor arrays 5L and 5R convert the images of an object (hereinafter referred to as the xe2x80x9cobject imagesxe2x80x9d) to electrical signals. The quantizer circuits 51L and 51R convert the electrical signals outputted from the photo-sensor arrays 5L and 5R to digital signals, The logic circuit 52 calculates a range signal (or a distance signal) based on the digital signals outputted from the photo-sensor arrays 5L and 5R. The images of an object T (hereinafter referred to as the xe2x80x9cobject imagesxe2x80x9d) are formed on the photo-sensor arrays 5L and 5R through the range finding lenses 1L and 1R arranged side by side such that the centers of the range finding lenses 1L and 1R are spaced apart for a base line length B.
The distance d from the range finding lenses 1L, 1R to the object T (hereinafter referred to as the xe2x80x9cobject distancexe2x80x9d) is calculated by the following formula (1) based on the principle of triangulation.
d=Bxc3x97fe/(X1+X2 )=Bxc3x97fe/Xxe2x80x83xe2x80x83(1)
Here, fe is the distance from the range finding lenses 1L and 1R to the sensor arrays 5L and 5R, that is equal to the focal length of the range finding lenses 1L and 1R. The X1 and X2 are the differences between the positions of the object images on the photo-sensor arrays 5L and 5R when the object T is at a finite distance and the positions of the object images on the photo-sensor arrays 5L and 5R when the object T is at the point of infinity distance. The length X (=X1+X2) is the relative shift length of the object images on the photo-sensor arrays 5L and 5R.
The structure of the conventional range finder integrated into a module mounted on a camera is shown in FIGS. 6(a) through 8. FIG. 6(a) is a top plan view of a conventional range finder module. FIG. 6(b) is a side plan view of the conventional range finder module. FIG. 6(c) is another side plan view of the conventional range finder module. FIG. 7 is an exploded perspective view of the conventional range finder module including the optical lens mount, the aperture mount and the sensor stage shown in FIGS. 6(b) and FIG. 6(c). FIG. 8 is a cross sectional view of the range finder module shown in FIGS. 6(a) through 6(c). Referring now to these figures, the range finder module includes an optical lens mount 1 including the pair of the range finding lenses 1L and 1R arranged side by side, an aperture mount 2 for guiding the rays impinging onto the range finding lenses 1L and 1R to the photo-sensor arrays 5L and 5R on the semiconductor sensor chip 5, and a sensor stage 3 including the semiconductor sensor chip 5 mounted thereon. The optical lens mount 1, the aperture mount 2 and the sensor stage 3 are made of plastic. These constituents are piled up and bonded at the bonding planes thereof such that they are combined into a unit.
The range finding lenses 1L and 1R are integrated into the optical lens mount 1 such that the range finding lenses 1L and 1R are positioned side by side. A pair of light guide spaces 2a are formed in the aperture mount 2 corresponding to the respective range finding lenses 1L and 1R. Aperture holes 2L and 2R, that determine the amount of the light impinging onto the semiconductor optical sensor chip 5, are formed in the respective light guide spaces 2a. The sensor stage 3 includes a lead frame 4 formed by insertion molding into the sensor stage 3. Bonding wires connect the lead frame 4 and the semiconductor optical sensor chip 5 mounted at a predetermined position on the sensor stage 3.
The space inside the range finder module is filled with a transparent filler 6 such as a transparent silicone gel, that seals the semiconductor optical sensor chip 5 and the vicinity thereof to prevent the pad of the sensor chip 5 and the bonding wires from being deteriorated by temperature change, moisture, thermal stress, foreign substances and such causes. FIG. 9 is a cross sectional view for explaining the method of injecting a transparent filler into the range finder module of FIG. 8. Referring now to FIG. 9, the back surface of the sensor stage 3 is open to provide an injection port for injecting the transparent filler and for absorbing thermal expansion and thermal contraction of the transparent filler. First, the range finder module of FIG. 8 is set upside down. A syringe containing a fluid transparent filler is set at the injection port in the open back surface of the sensor stage 3. The transparent filler 6 is injected into the range finder module through the gap between semiconductor optical sensor chip 5 and the sensor stage 3. The transparent filler 6, that has flowed into the inside space surrounded by the optical lens mount 1, the aperture mount 2 and the sensor stage 3, fills the inside space. Further, the transparent filler 6 covers the semiconductor optical sensor chip 5. Then, a heat treatment is conducted to cure the transparent filler 6. The amount of the transparent filler 6 is controlled such that the transparent filler 6 is injected up to the level of the open back surface of the sensor stage 3 at the end of the transparent filler injection.
The transparent filler injection into the conventional range finder module as described above causes the following problems. When injection speed variation and injection amount variation are caused during injecting the transparent filler 6, the light guide spaces 2a in the aperture mount 2 are not completely filled with the transparent filler 6 sometimes. When the light guide spaces 2a are not filled with the transparent filler 6 completely, voids are caused by heat treatment in the field of view between lenses 1L, 1R and the optical sensor arrays 5L, 5R. As a result, the object images are not formed correctly on the photo-sensor arrays 5L and 5R.
The present inventors have found the causes for the voids in the transparent filler. As shown in FIG. 9, the transparent filler 6 is injected from one injection port. However, the inside space of the range finder module to be filled with the transparent filler 6 forks to the right light guide space and the left light guide space in the aperture mount 2. Since the front end of the aperture mount 2 is in contact with the optical lens mount 1 and since the light guide spaces 2a are separated from each other by a partition wall 2b as shown in FIG. 8, the light guide spaces 2a are shaped with respective pockets and the middle portions of the pocket-shaped light guide spaces 2a are narrowed by the aperture holes 2L and 2R.
During the transparent filler injection described in FIG. 9, the air in the spaces replaced by the transparent filler 6 may escape upward through the aperture holes as far as the transparent filler flows little by little into the space between the optical lens mount 1 and the aperture mount 2 through the aperture holes 2L and 2R. However, when the transparent filler flowing onto the aperture holes 2L and 2R closes the narrow aperture holes 2L and 2R while unfilled regions are still remaining in the space between the optical lens mount 1 and the aperture mount 2, the air in the unfilled regions has no way to escape and the air is enclosed in the regions below the aperture holes 2L and 2R. The enclosed air prevents the transparent filler 6 from being injected further and bubbles are caused in the transparent filler layer.
Since the transparent filler, injected from the injection port of the sensor stage 3, is distributed to the right and left light guide spaces 2a, imbalance is caused between the amount of the transparent filler flowing into the right light guide space and the amount of the transparent filler flowing into the left light guide space. When the surface of the transparent filler flowing into one of the light guide spaces reaches the level of the aperture hole in advance of the surface of the transparent filler flowing into the other light guide space, the transparent filler, that has flowed into that one light guide space may overflow to the other light guide space. The overflowing transparent filler closes the narrow aperture hole and causes an unfilled region or unfilled regions.
When an unfilled region or unfilled regions are caused, the transparent filler, of an amount corresponding to the volume of the unfilled region or the unfilled regions, leaks from the injection port of the sensor stage 3. The leaking transparent filler sticks to the outer wall of the plastic module and terminal portion of the lead frame 4 and impairs the external appearance of the range finder module. Accordingly, it would be desirable to provide a range finder that obviates the problems described above. It would be further desirable to provide a range finder having an improved module structure, that facilitates filling a transparent filler uniformly into the entire light guide spaces neither leaving any unfilled region nor impairing the characteristics thereof.
According to an aspect of the invention, there is provided a range finder including: an optical lens mount including a pair of range finding lenses arranged side by side; an aperture mount including a pair of light guide spaces, the light guide spaces being arranged side by side corresponding to the range finding lenses, a pair of aperture holes for limiting the rays through the range finding lenses, the aperture holes being arranged side by side corresponding to the range finding lenses, and a partition wall separating the light guide spaces; a sensor stage mounting a semiconductor sensor chip thereon, the semiconductor sensor chip measuring the distance between an object and the image of the object formed thereon through the range finding lenses; the optical lens mount, the aperture mount and the sensor stage being piled up and combined into a unit such that a module of the range finder is formed; a transparent filler filling the space inside the module of the range finder such that the semiconductor sensor chip is sealed; and the aperture mount including a channel of flow formed across the partition wall, the channel of flow connecting the light guide spaces arranged side by side. Advantageously, the channel of flow is a U-shaped groove (hereinafter referred to as a xe2x80x9cU-groovexe2x80x9d) formed across the partition wall on the open end side of the aperture mount facing to the range finding lenses.
When a transparent filler is injected into the space in a range finder module from the injection port of the range finder module set upside down, the space in the range finder module is filled with the transparent filler completely without leaving any unfilled region. In detail, the transparent filler injected from the injection port is divided into two streams, that further flow into the light guide spaces arranged side by side. Due to the difference between the amounts of the transparent filler flowing into the light guide spaces, a difference is caused temporarily between the levels of the transparent filler surfaces in the light guide spaces. However, since the transparent filler flows through the channel of flow, connecting the light guide spaces to each other, from one of the light guide spaces to the other due to the gravitational force, levels of the transparent filler surfaces are equalized.
Therefore, the rising levels of the transparent filler surfaces in the light guide spaces are always equalized to each other. Thus, the transparent filler flows smoothly in the space inside the range finder module, never closes the aperture hole downward and fills the space inside the range finder module completely without leaving any unfilled region. Since the transparent filler surface rises uniformly around the semiconductor optical sensor chip, all the predetermined amount of the transparent filler is injected without causing any leakage from the injection port. Moreover, since the transparent filler is injected smoothly, the period of time necessary to inject the transparent filler is shortened.
Advantageously, the range finder further includes shield walls arranged in the channel of flow (or U-groove), the shield walls preventing a ray, that has entered the channel of flow (or U-groove) through one of the range finding lens, from entering the light guide space on the other side through the channel of flow (or U-groove). Advantageously, the shield walls includes one or more walls protruding from one of the side walls of the channel of flow (or U-groove) and one or more walls protruding at different locations along the channel of flow from the other side wall of the channel of flow (or U-groove), the side walls of the channel of flow facing opposite to each other. Advantageously, the range finder further includes a space between the shield walls and the optical lens mount.
A part of the rays, having high incident angles and refracted by one of the range finding lenses, propagates straight through the light guide space or is reflected by the wall of the light guide space to the channel of flow (or U-groove). However the ray propagating straight through the light guide space or reflected by the wall of the light guide space to the channel of flow (or U-groove) is interrupted by the shield walls arranged in the channel of flow (or U-groove), prevented from further entering the adjacent light guide space, reflected or absorbed by the shield walls and finally extinguished. If the shield walls were not disposed, a part of the rays, that have entered the light guide space, further enters the adjacent light guide space through the channel of flow (or U-groove), causing stray light. The stray light prevents object images from being formed correctly on the photo-sensor arrays, causing low accuracy of range finding. The shield walls prevent stray light from causing errors in range finding.
By positioning the shield walls such that some walls protruding from a side wall[s] of the channel of flow (or U-groove) and the other walls protruding from the other side wall of the channel of flow (or U-groove), the channel of flow (or U-groove) shaped with a labyrinth connects the light guide spaces with each other. The channel of flow (or U-groove) facilitates injecting the transparent filler smoothly into the range finder module.